In the art of roll type straighteners, it is well known to employ a straightener apparatus having combinations of contoured rolls for the purpose of straightening lengths of metal stock of circular cross section, for example, steel rods or pipe. Such straightening apparatus has often comprised, for example, a five-roll arrangement, in which a pair of contoured support rolls are positioned, respectively above and below the workpiece with their axes skewed to one another in parallel planes and in addition skewed to the axis of the workpiece being supported thereby. A second pair of similarly disposed support rolls is spaced from this first-mentioned pair of rolls along the axis of the workpiece being supported thereby, and an unopposed contoured pressure roll is disposed intermediate the two pairs of support rolls to engage the workpiece and, in conjunction with the support rolls, to apply a bending moment thereto. Another such machine has a six-roll cofiguration similar to that described above, but in which a pair of opposed pressure rolls is located intermediate the two pairs of support rolls.
Typically, one of the rolls in each pair of support rolls is a driven roll, while the other is an idler. The work preferably engages each support roll in line contact along the length of the roll body whereby, as the driven rolls turn, the workpiece is rotated axially and advanced in the axial direction through the straightener in the well-known manner.
These and other configurations of roll straighteners have customarily utilized opposed pairs of axially spaced-apart support rolls to support the stock being worked, and suitable roll contour for the support roll pairs has long been a primary concern in the art. For example, U.S. Pat. No. 1,649,204 of Wise discloses a roll surface profile for the rolls of a straighener generally of the type specified above.
In a necessary function of the support roll pairs in a contoured roll straightener of the type described to provide lateral restraint for the workpiece in order that the bending movement applied to the workpiece will not tend to bend it in planes other than in the vertical plane of its own axis. In addition, in the absence of proper lateral restraint provided by the support roll pairs, the applied bending movement may cause the workpiece to progress through the straightener rolls along a path skewed from the proper path of travel. This may result in unnecessary marring of the workpiece surface, increased energy demands for a given straightening operation, and accelerated straightener roll wear.
In order to provide the requisite lateral restraint, various support roll pair configurations have been utilized. In general, the proper lateral restraint for a given roll pair, positioned in the usual manner above and below the workpiece, may be considered in terms of the angle with respect to vertical of the net restraining force applied by a support roll in cross-sectional planes generally perpendicular to the workpiece axis. The lateral restraining force is distributed along the line of contact between roll and workpiece, and acts perpendicularly to the mutual tangent therebetween.
The angle from vertical of the net restraining force is a function of roll diameter and the axial distance from the roll throat. That is, at the roll throat, the force applied by a support roll in a straightener of the type specified is vertically directed and provides no lateral component, but at successively greater distances from the roll throat along the line of contact with the workpiece, the angle with respect to vertical of the force applied by the support roll increases to a maximum angle adjacent the roll ends. Therefore, the lateral component of a constant supporting force would increase from zero at the roll throat to a maximum at the roll ends.
In order to provide proper lateral support for the workpiece, the rolls of each support roll pair must be so contoured and positioned with respect to one another that the resultant of the supporting forces applied thereby to the workpiece provide a lateral vector component to resist the lateral deflection tendency that would otherwise be inherent in the use of skewed, contoured rolls for workpiece support.
Various configurations of support roll pairs have been proposed in the prior art to provide the necessary lateral restraint. For example, one prior approach has been to utilize a pair of mutually-centered rolls of different diameters and length to provide workpiece support and the requisite lateral restraint. One shortcoming of this approach has been the need for manufacture of at least two distinct roll designs for each support roll pair. In addition, as the rolls of each such pair of of differing length, the required lateral restraint is provided only by so much of the lines of contact of each roll as are mutually coextensive or oveerlapping along the axial extent of the workpiece. The longer roll projects beyond the ends of the shorter roll and its engagement with the workpiece in these non-overlapping regions does not provide suitable lateral restraint for the workpiece. Indeed, it may contribute to undesirable lateral deflection of the workpiece.
Another prior approach has involved use of a roll pair in which the rolls are offset from one another, such that there is a displacement along the axis of the workpiece between the throats of the two rolls of each pair. This approach, like that described above, suffers in that the lateral restraint is provided only in the zone of overlap of the lines of contact of each roll with the workpiece. Accordingly, a significant portion of each such roll is ineffective for proper lateral restraint of the workpiece, and may be a cause of lateral deflection.
In the prior art, it has been considered desirable that the support rolls of a contoured roll straightener perform a rounding up operation on the stock passing therethrough, as this was one way in which to enhance product quality by taking advantage of an inherent capability of some configurations of support roll pairs. This has been possible in prior roll pairs only if the roll throats were centered with respect to each other. Accordingly, another shortcoming of prior offset roll pairs has been the loss of the beneficial rounding up capability.